IMHO A family of WYSIWYG buttons in a 'code editor' g3ets you output like you get from Word. A

mess.
<b>,<i> are clean because they are basic.
Learn how to Link and use a CSS. It really is easy once you unlearn all the
bad habits learned using HTML2 or WYSIWYG editors like Word.
Take a few and
reverse engineer a few similar books that use CSS.
IMHO Sigil's 'Goto Link or style excels here. Right-click on the
class=: Select: Goto Link or style: Presto, you are at that selector in the proper CSS (A complex book can have many CSS files, you are only concerned with the ones linked to the current page)
The mythical; One Size Fits All CSS only applies to content YOU CREATE from Scratch.